I've had the same problem, but on this computer I'm stuck with an older version. Downloads would disappear into the ether. Then I discovered I could find them if I highlighted a completed download and selected, Open folder. I could then move the files to a new folder, but I could never find where the files were hiding. At some point, I found that every time I rebooted, I had to re-set my download folder, because the app won't remember the previous setting.